A sapphire/gallium nitride laminate, which is useful for a light emitting device (eg., LED, LD) or other electronic devices as a substrate, has been conventionally prepared by growing gallium nitride on a sapphire substrate using metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), etc. The sapphire/gallium nitride laminate suffers from bending deformation due to interfacial strain caused by the differences in the lattice parameter and thermal expansion coefficient between sapphire and gallium nitride. The degree of the bending deformation increases as the thickness of a gallium nitride (GaN) film increases, as can be seen in FIG. 1. Such bending deformation adversely affects the quality and productivity of an electronic device comprising the laminate as a substrate.
U.S. Pat. No. 6,528,394 discloses a method for growing gallium nitride having an interface layer with an embossed shape between a GaN film and a sapphire substrate by carrying out a first nitridation, a surface-treatment with ammonia (NH3) and hydrogen chloride (HCl) and a second nitridation, in succession, to form an aluminum nitride (AlN) interface layer, before the growth of gallium nitride.
On studying a sapphire/gallium nitride laminate having a reduced bending deformation and a sufficiently thick gallium nitride layer, the present inventors have found that the bending deformation can be further reduced by controlling the number and size of the embossings formed on an AlN interface layer between the GaN film and the sapphire substrate.